A conventional four pole permanent magnet electric motors typically uses four brushes. For example, FIG. 1A illustrates a stator 100 of a four pole permanent magnet electric motor having four brushes 102 for which to contact a commutator comprising a plurality of commutator bars. FIG. 1B illustrates a rotor 104 for the four pole permanent magnet electric motor, wherein rotor 104 has twenty rotor teeth 106 defining twenty rotor grooves 108.
Referring also to FIG. 1C, brushes 102 are configured to interface with a plurality of commutator bars 110 on rotor 104. A plurality of windings 112 are connected to the commutator bars 110 and wrapped around rotor teeth 106 and accommodated in rotor grooves 108. During operation, current is transferred from brushes 102 to windings 112 via commutator bars 110, thereby generating magnetic fields interacting with a plurality of magnetic components (e.g., permanent magnets) mounted on stator 100 driving rotor 104 to spin relative to the stator 100. FIG. 1C illustrates a schematic diagram of an exemplary layout for windings 112 arranged in a lap winding configuration. For ease of understanding, FIG. 1C illustrates commutator bars 110 and rotor teeth 106 linearly.
For certain applications, it is desirable to reduce the number of brushes of the electric motor, thereby decreasing manufacturing costs and lowering the complexity of assembly. For example, FIG. 2A illustrates a permanent magnet electric motor 200 with four magnetic poles, but having only two electric brushes (21 and 23) instead of four.
One method of reducing the number of brushes is to use an equalizer selectively connecting the commutator bars of the electric motor. However, the equalizer also adds manufacturing costs and assembly complexity. For example, FIG. 2B illustrates a schematic diagram of an exemplary layout for windings 112 using equalizer 114.
Another method of reducing the number of brushes in the electric motor is to utilize wave windings instead of lap windings. However, typical wave winding configurations require the commutator to have an odd number of commutator bars, requiring a separate commutator and rotor design from conventional motors, potentially increasing manufacture and assembly costs.
Accordingly, it would be advantageous to reduce the manufacturing costs and assembly complexity of an electric motor by utilizing a reduced number of brushes and a commutator having an even number of commutator bars.